Engine liquid cooling system

ABSTRACT

A method of limiting pressure in a liquid cooling system of an internal combustion engine when the engine overspeeds, such as when an engine brake is applied.

TECHNICAL FIELD

This disclosure relates to a liquid-cooled internal combustion engine of the type which propels a motor vehicle.

BACKGROUND

A liquid-cooled internal combustion engine of the type which propels a motor vehicle typically comprises a temperature-controlled valve, an example of which is commonly referred to as an engine thermostat, for controlling flow of engine coolant to a radiator. The thermostat comprises an inlet to which coolant, which has been pumped through a system of coolant passageways in an engine cylinder block and cylinder head by a coolant pump, is communicated. The thermostat has two outlets, one to the radiator, the other to a coolant return passage which leads to the suction side of the coolant pump.

When the engine begins running from cold-start, the coolant pump pumps coolant through the system of coolant passageways in the engine cylinder block and cylinder head to the thermostat inlet while the thermostat closes the one outlet to the radiator and opens the other outlet to the coolant return passage. That prevents heat from being wasted by rejection to air passing through the radiator until the engine reaches normal operating temperature range. Once the engine has warmed to normal operating temperature, the thermostat opens the one outlet to the radiator and closes the other outlet to the coolant return passage to maintain coolant temperature within a normal engine operating temperature range.

An example of an engine-driven coolant pump is a centrifugal volute pump which comprises an engine-driven impeller which converts input power from the engine into kinetic energy in the liquid coolant by accelerating coolant which enters through an eye of the impeller and is accelerated radially outward from eye. That creates a vacuum in the eye continuously drawing coolant into the pump. The faster the impeller revolves, the greater the velocity to which coolant is accelerated. This is described by the Affinity Laws. Coolant leaving the impeller is obstructed by resistance present in the pump casing, the engine cylinder block and the engine cylinder head, decelerating the coolant. As the coolant flow slows, some of its kinetic energy is converted to pressure energy. The pressure increases with pump speed, and may increase beyond tolerable pressure limits of components, such as when the engine overspeeds.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to an internal combustion engine which has a normal operating speed range up to a maximum engine operating speed and which may overspeed when the engine is operated in certain ways.

The engine comprises engine structure comprising engine cylinders within which combustion of fuel occurs to generate heat, a first portion of which operates the engine and a second portion of which heats the engine structure, and internal coolant passageways through which liquid coolant circulates to absorb heat from the engine structure.

A liquid cooling system comprises a pump driven by the engine for circulating liquid coolant through the internal coolant passageways, a radiator at which heat is rejected from liquid coolant flowing through the radiator to air flowing through the radiator, a first coolant return passage for liquid coolant flow to by-pass the radiator, and a first control valve having an inlet open to a first outlet of the internal coolant passageways for controlling coolant flow from the first outlet of the internal coolant passageways through the radiator and the first coolant return passage.

The liquid cooling system also comprises a second coolant return passage for liquid coolant flow from the internal coolant passageways to by-pass both the first control valve and the radiator. The second coolant return passage comprises a second control valve having an inlet open to a second outlet of the internal coolant passageways which is separate from the first outlet of the internal coolant passageways. The second control valve controls flow of coolant from the second outlet of the internal coolant passageways back to the pump.

An engine controller controls the second control valve to control flow of coolant through the second control valve.

The present disclosure also relates to a method of limiting pressure at a location in the liquid cooling system.

The method comprises using the first control valve to control coolant flow from the first outlet of the internal coolant passageways through the radiator and the first coolant return passage to the pump; and using the second control valve to control coolant flow from the second outlet of the internal coolant passageways to by-pass both the first control valve and the radiator.

The foregoing summary, accompanied by further detail of the disclosure, will be presented in the Detailed Description below with reference to the following drawings that are part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a representative cooling circuit of a liquid-cooled internal combustion engine which propels a motor vehicle.

FIG. 2 is a schematic diagram representative of a portion of an engine controller which is operatively associated with the cooling circuit of FIG. 1.

FIG. 3 is a two-dimensional graph plot useful in understanding the operative association of the engine controller of FIG. 2 with the cooling circuit of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion propulsion engine 10 of a motor vehicle such as a large truck. Engine 10 comprises a liquid cooling system (LCS) 12 having various flow paths through which liquid coolant circulates, including a system of internal coolant passageways 14 in engine structure 16 which contains engine cylinders (not shown) within which combustion of fuel occurs to operate engine 10. Engine structure 16 typically comprises a cylinder block overlying an engine crankcase, and depending on the particular cylinder block configuration, one or more cylinder heads, intake manifolds, and exhaust manifolds, none of which are individually marked in FIG. 1.

Liquid coolant is circulated through LCS 12 by an engine-driven coolant pump 18, which comprises a suction inlet 18S and a pressure outlet 18P. Coolant pump 18 may be a centrifugal volute pump, as described earlier. As pump 18 operates, it pumps coolant through pressure outlet 18P and into internal coolant passageways 14 where the circulating coolant absorbs engine heat.

Engine structure 16 comprises a first outlet 20 for coolant which has passed through internal coolant passageways 14. Engine structure 16 also comprises a second outlet 21 for coolant which has passed through internal coolant passageways 14. Second outlet 21 is separate from first outlet 20 and may be situated at a different location of engine structure 16 from the location of first outlet 20.

LCS 12 further comprises a first control valve 22 for controlling whether coolant which has passed from internal coolant passageways 14 through first outlet 20 flows through a radiator 24 before returning to suction inlet 18S or whether coolant by-passes radiator 24 by flowing through a first coolant return passage 26 directly back to suction inlet 18S.

When engine coolant temperature is less than what is considered normal engine operating temperature range, first control valve 22 closes a first of two valve outlets 28 to radiator 24 and opens a second of two valve outlets 30 to first coolant return passage 26, causing coolant to by-pass radiator 24 by flowing through first coolant return passage 26 directly back to suction inlet 18S. By not rejecting heat to radiator 24 after engine 10 has been cold-started, the engine is able to reach normal engine operating temperature range more quickly.

When engine coolant temperature reaches normal engine operating temperature range, first control valve 22 opens valve outlet 28 to radiator 24 and valve closes outlet 30 to first coolant return passage 26, causing coolant to flow through radiator 24 before returning to suction inlet 18S. Absorbed heat is rejected to air passing through radiator 24 with heat transfer occurring by ram air effect and/or by a fan or fans (not shown) pulling or pushing air through radiator 24. Rejection of engine heat to air passing through radiator 24 maintains engine operation in normal engine operating temperature range.

First control valve 22 is typically referred to by the generic descriptor “engine thermostat.” Various types of engine thermostats are known.

Radiator 24 comprises a top tank 32, a bottom tank 34, and multiple tubes 36 through which coolant can flow from top tank 32 to bottom tank 34. A passage 38 communicates outlet 28 to top tank 32, and a passage 40 communicates bottom tank 34 to suction inlet 18S.

FIG. 1 shows that LCS 12 also comprises a second control valve 42 and a second coolant return passage 44. Second control valve 42 has an inlet open to second outlet 21. Some coolant from the system of internal coolant passageways 14 can pass into and through second control valve 42 when second control valve 42 is open, with coolant leaving through a valve outlet to enter and flow through second coolant return passage 44 back to suction inlet 18S.

An engine controller 45, a portion of which is shown in FIG. 2, controls second control valve 42. That portion comprises a software logic section 46 which processes data from several maps including a valve control map 48, an engine load map 50, an engine speed map 52, and a coolant temperature map 54.

Logic section 46 controls coolant system pressure by operating second control valve 42 from closed to open under certain conditions.

FIG. 3 shows a two-dimensional graph plot in non-dimensional units where the horizontal axis represents engine speed and the vertical axis represents pressure in top tank 32. A trace 56 shows that as engine speed increases over a normal operating speed range 58 up to a maximum engine operating speed 60 for the particular engine, pressure in top tank 32 also increases to a pressure P1 when outlet 30 of first valve 22 is closed to coolant return passage 26.

For any of one or more reasons, engine speed can become larger than maximum engine operating speed 60. For example, actuation of certain types of engine brakes and the temporary stoppage of engine fueling which accompanies engine brake application 62 can under certain conditions cause the engine to overspeed.

By a programmed boundary condition, speed overrun, i.e. an increase in engine speed to a speed greater than the maximum engine operating speed, can be detected, and via logic section 46, second control valve 42 can be operated from closed to open to limit pressure throughout LCS 12, including pressure at outlet 28 and hence the pressure in top tank 32 as indicated by trace 64 in FIG. 3. In the absence of this limiting, the pressure in top tank 32 would continue to increase as indicated by trace 66 in FIG. 3.

That way of controlling second control valve 42 comprises keeping second control valve 42 closed until engine 10 overruns to a speed greater than the maximum engine operating speed, such as when an engine brake is applied, whereupon an actuator 68 of second control valve 42 is operated to open second control valve 66 and keep it open until engine overrun ceases whereupon second control valve 66 is closed.

Another way comprises keeping second control valve 66 closed until pump outlet pressure is indicated to be greater than a predetermined pressure whereupon actuator 68 is operated to open second control valve 42 and keep it open until pump outlet pressure ceases to be indicated greater than the predetermined pressure engine whereupon second control valve 42 is closed. The predetermined pressure limit may or may not be correlated with an engine speed corresponding to maximum engine operating speed in the normal engine operating speed range. Pump outlet pressure can be inferred from data processed by engine controller 45 and/or measured by a pressure sensor.

Both ways are effective to limit pressure applied not only to the radiator but also to other components which include the pump casing, the engine cylinder block and the engine cylinder head, to tolerable limits for the respective components. 

What is claimed is:
 1. An internal combustion engine which comprises: engine structure comprising engine cylinders within which combustion of fuel occurs to generate heat, a first portion of which operates the engine and a second portion of which heats the engine structure, and internal coolant passageways through which liquid coolant circulates to absorb heat from the engine structure; a liquid cooling system comprising a pump driven by the engine for circulating liquid coolant through the internal coolant passageways, a radiator at which heat is rejected from liquid coolant flowing through the radiator to air flowing through the radiator, a first coolant return passage for liquid coolant flow to by-pass the radiator, and a first control valve having an inlet open to a first outlet of the internal coolant passageways for controlling coolant flow from the first outlet of the internal coolant passageways through the radiator and the first coolant return passage; a second coolant return passage for liquid coolant flow from the internal coolant passageways to by-pass both the first control valve and the radiator, the second coolant return passage comprising a second control valve having an inlet open to a second outlet of the internal coolant passageways which is separate from the first outlet of the internal coolant passageways, the second control valve controlling flow of coolant from the second outlet of the internal coolant passageways back to the pump; and an engine controller for controlling the second control valve to control flow of coolant through the second control valve.
 2. The internal combustion engine as set forth in claim 1 in which the engine controller is effective to operate the second control valve from closed to open in response to engine speed increasing to a speed greater than maximum engine operating speed within a normal engine operating speed range and from open to closed in response to engine speed decreasing to a speed less than maximum engine operating speed within the normal engine operating speed range.
 3. The internal combustion engine as set forth in claim 2 including an engine brake which when applied and when combustion of fuel in the engine cylinders is temporarily stopped, causes engine speed to increase to a speed greater than the maximum engine operating speed within the normal engine operating speed range.
 4. The internal combustion engine as set forth in claim 1 in which the engine controller operates the second control valve from closed to open when pressure at a location in the liquid cooling system is indicated to have become greater than a predetermined pressure and from open to closed when pressure at the a location in the liquid cooling system is indicated to have become not greater than the predetermined pressure.
 5. The internal combustion engine as set forth in claim 1 in which the engine controller comprises a software logic section and maps which provide data for processing by the software logic section to control the second control valve.
 6. In a liquid cooling system of an internal combustion engine having a pump which is driven by the engine to circulate liquid coolant through internal coolant passageways in engine structure to absorb heat from combustion of fuel occurring within engine cylinders within the engine structure to operate the engine over a normal operating speed range up to a maximum engine operating speed, a method of limiting pressure at a location in the liquid cooling system, the method comprising: using a first control valve to control coolant flow from a first outlet of the internal coolant passageways through a radiator and a first coolant return passage to the pump; and using a second control valve to control coolant flow from a second outlet of the internal coolant passageways which is separate from the first outlet of the internal coolant passageways through a second coolant return passage which returns to the pump and by-passes both the first control valve and the radiator.
 7. The method as set forth in claim 6 including operating the second control valve from closed to open in response to engine speed increasing to a speed greater than maximum engine operating speed within a normal engine operating speed range and from open to closed in response to engine speed decreasing to a speed less than maximum engine operating speed within the normal engine operating speed range.
 8. The method as set forth in claim 7 including applying an engine brake to cause engine speed to increase to a speed greater than maximum engine operating speed within the normal engine operating speed range. 